This invention relates to a piston internal-combustion engine and, more particularly, to a piston internal combustion engine operable in a supercharging manner by at least one group of switchable exhaust gas turbochargers.
For exhaust-gas-charged piston internal-combustion engines, the charging conditions in the partial-load operation of the engines can be improved in a known manner by operating several exhaust gas turbochargers. The exhaust gas turbochargers are operated in parallel when the offering of exhaust gas is high. Some of the exhaust gas turbochargers are shut down by blocking their exhaust gas feeding pipe when the amount of occurring exhaust gas is reduced. Thus, in the partial-load operation of the piston internal-combustion engine, the exhaust gas quantity is distributed to a small number of exhaust gas turbochargers. As a result, the exhaust gas turbochargers again operate in proximity of their design point and therefore with better efficiency. This results in a higher charge pressure, and makes available a larger amount of charge air. Because of the higher air excess, the combustion sequence is improved, the fuel consumption is lowered, and a smoke-free operation is achieved. This is also the case for piston internal-combustion engines which are designed for a higher medium pressure.
A known arrangement of this type is described in the German Patent Document DE 30 05 655 C2. The arrangement has the disadvantages resulting from the still considerable space requirement necessary because of the requirement of a finely graduated adaptation of the charge air supply to the offered exhaust gas during partial load of the piston internal-combustion engine. In particular, when the piston internal-combustion engines are of a small size, difficulties occur in the housing of several exhaust gas turbocharger groups.
There is therefore needed a group of switchable exhaust gas turbochargers which optimize the space requirement in connection with a finely graduated adaptation on the turbine side of the exhaust gas as well as on the compressor side to the charge air requirement of the piston internal-combustion engine.
According to the present invention, this need is met by at least three exhaust gas turbochargers fastened next to one another to the side wall of a gas-tight box. The exhaust gas collector of the engine is connected with a first exhaust gas inlet of a first exhaust gas turbine of the first exhaust gas turbocharger. The first exhaust gas turbocharger is centrally located among the three exhaust turbochargers and an exhaust gas flow divider is rotatably arranged on the first exhaust gas outlet such that, in a first position, the exhaust gas flow divider connects the first exhaust gas outlet of the central exhaust gas turbocharger with the second exhaust gas inlets of the two adjacent exhaust gas turbochargers and, in a second position, the exhaust gas flow divider connects the first exhaust gas outlet of the central exhaust gas turbocharger directly to an exhaust pipe. Because of the physical closeness of the three exhaust gas turbochargers disposed next to one another, on the compressor side as well as on the turbine side, very short line connections are obtained for the switching-together of the exhaust gas turbochargers among one another.
The present invention further provides an exhaust-gas switch-over device arranged between the exhaust gas collector and the first exhaust gas inlet of the central exhaust gas turbocharger, for full and partial loading of the first exhaust gas turbine.
Another advantage of the present invention includes the use of a charge-air switch-over device arranged in front of a first turbine wheel inlet of a first charge air compressor of the central exhaust gas turbocharger. The charge-air switch-over device includes an outflow connection corresponding with the first turbine wheel inlet; at least two inflow connections; and a closing part interacting with the at least two inflow connections.
In a preferred embodiment of the invention, one inflow connection of the charge-air switch-over device is arranged coaxially with respect to the outflow connection and the two other inflow connections are arranged approximately tangentially with respect to the outflow connection on the charge-air switch-over device.
A further advantage of the invention provides two flaps which, in a first position, close off the one coaxial inflow connection, and, in a second position, block off the two other tangential inflow connections.
Yet another embodiment of the present invention comprises second charge air pressure lines of the two adjacent exhaust gas turbochargers which are connected with one of the at least two inflow connections of the charge-air switch-over device. A first charge air pressure line of the central exhaust gas turbocharger is connected with a charge air collector of the piston internal-combustion engine.
The principal advantages achieved by the invention are that a very compact arrangement of a group of switchable exhaust gas turbochargers, together with all lines and switching elements, is obtained. Further, by means of this arrangement, a charge air supply of the piston internal-combustion engine is achieved that can be switched in multiple steps, and that the advantages of the variable charge air supply can be utilized also for small sized piston internal-combustion engines.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.